Design and optimisation of cushioning structure of hydraulic free‐piston engine

Abstract

The velocity of the free-piston assembly (FPA) of the hydraulic free-piston engine (HFPE) is very high, which is up to 10 m/s. In order to avoid the collision of the FPA to the cylinder head when the FPA moves towards the dead centres, the cushioning device must be involved. A cushioning structure which combines the sidestep-shape cushion and flute-shape cushion is proposed according to the working principle of the HFPE. The mathematical model of the cushioning is set up, and key parameters are obtained. AMESim is employed to analyse the cushioning process and the influence of the key parameters on the cushioning process. The optimised parameters are obtained according to the simulation. The test rig is established to verify the effectiveness of the cushioning structure according to the optimised parameters. The experiment results show that the proposed cushioning structure is reliable. The maximum pressure during the cushioning process is 19 MPa, and cushioning time is 12 ms. The cushioning structure has little influence on the starting process of HFPE.